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Electrical questions thread

 

Silver Member
Username: Cwruck

Post Number: 120
Registered: Feb-10
hi guys i want to start a thread where you can come to and get answers for all of your electrical questions. There are many intelligent people here and i know i have many questions myself i would like to get answered, so any comments is appreciated.
first off i was wondering if you are running an amp that can do 1500 watts rms which draws approx. 140 amps at full current in a car with a stock alt rated at 80 amps obviously the alt is going to fail at max draw and drop in voltage letting the battery(s) take over to bring the voltage back up to stable conditions. what will happen when you do turn the volume down and the current draw drops down to 20 or so amps, and the alt takes over, does the alt work at max performance to recharge that battery? or does it do so only if the battery is completely drained to where it can not bring the voltage back up if it needed to do.
if it does recharge the battery even if it is not fully drained how long on average does it take the fully recharge the battery?
I can understand the time of course would depend on the size of the battery and how much "juice" it has left it in. but i was just wondering an approx time.
 

Platinum Member
Username: Glasswolf

Lexington, SC USA

Post Number: 13456
Registered: Dec-03
when the alternator is drawn beyond it's peak capacity, the battery will only hold for so long, depending on it's Ah rating and hysteresis curve. At extremely high current draw like that, the battery would fail fairly fast as well, and voltage rails will drop below 11VDC, which will cause the amplifier signal to clip at which time you'll start ramping up heat across the voice coils of the drivers, and causing damage.

In a typical (no stereo system) car, the battery is there to start the engine.
Once the engine is running on internal combustion, the crankshaft, via accessory belts, spins the alternator, which, dependent on rotor speed (dependant on pully ratio and engine RPM) will produce a specified amount of current. The alternator's output varies not only by rotor speed and pully ratio, but also by temerature. We'll pretend for this discussion, that the Alt in question is at full output (void of engine RPM, temperature, etc)

When the engine is running, the alternator puts out AC voltage.
the voltage regulator rectifies this to DC voltage, which is used to power electrical devices in the car, and to recharge the car's starter battery.
The reason this works is because the battery has a chemical voltage of 12.6VDC.
The alternator has an "above idle) output of 13.8 to 14.4VDC, which places a forward voltage bias across the battery, and due to the chemical composition of the battery, causes the battery to recharge *as long as the alternator voltage is higher than that of the battery.*

When your audio system drains all available current from the alternator, it then keeps the alternator running at full current output for as long as the system demands equal to or more current than the alternator can provide.
When this happens, the battery will supply what voltage is can, for as long as it can.

Now you turn off the stereo, and the battery is down to, let's say 10 volts. Now the alternator sill put out whatever current is demanded from it by the remaining devices still using electricity (your ignition system for example.) and the alternator voltage will pop back up to it's above idle voltage )(say 13.8VDC) which in turn begins recharging the battery at a rate determined by the alternator output voltage, the battery's current state, and the battery's hysteresis curve for charging. (the rate it charges over a period of time as per it's voltage at that time)

voltage is constant.
amperage from teh alternator is supplied "on demand" as it is needed by things drawing that current.

Think of it like a roll of toilet paper. The roll may have 50000 sheets on it, and those sheets will remain there as "potential use" until someone grabs the end of the roll and starts to pull sheets from the roll. The more sheets the person needs, the more they will pull from the roll. The roll will not put any sheets out by itself. It only supplies what's taken by other people.
 

Platinum Member
Username: Glasswolf

Lexington, SC USA

Post Number: 13457
Registered: Dec-03
http://www.glasswolf.net/papers/index.html

there is some stuff there under electrical and miscellaneous that may help to an extent.
 

Gold Member
Username: Frkkevin

Team DLSSuperNatural...

Post Number: 7677
Registered: Nov-05
What if its non tear toilet paper :P

Good explanation and analogy
 

Platinum Member
Username: Glasswolf

Lexington, SC USA

Post Number: 13468
Registered: Dec-03
non tear? you mean that Russian stuff with the wood bark in the sheets? That stuff scares me, man. It's like wiping with #220 grit sandpaper.
 

Gold Member
Username: Frkkevin

Team DLSSuperNatural...

Post Number: 7678
Registered: Nov-05
I was talking about the stuff from gag shops but haha.. that stuff would scare me as well
 

Diamond Member
Username: Wingmanalive

Www.stainles... .ecrater.com

Post Number: 22796
Registered: Jun-06
One thing I hate to read over and over again is how so many ppl want to amend their current charging problems with more batteries. There is no replacement for electrical production. Simply put, if you don't produce what you use it WILL haunt you in the end. Usually by over taxing the stock or lame alternator by many times its' intended use. Adding an additional batt does NOT rectify an inadequate charging system.


Kinda like buying a big house on a little budget. When it comes time to furnish all those rooms you'll realize the imbalance in the equation. Owning a home involves a great deal more than just paying the mortgage, just like the electrical system in your car. There's maintenance, insurance, utilities, improvements, ect, all of which needs accounted for in the big picture.

Maybe that's why I choose to bump it in my home now instead of my car. To save $$.
 

Platinum Member
Username: Glasswolf

Lexington, SC USA

Post Number: 13474
Registered: Dec-03
hahaha yeah like buying home audio is cheaper.. LOL Tell that to my Krell and Aragon amplifiers, and my KEF Reference and MartinLogan speakers. *sigh* I could have done nice car systems ten times over for what some of that cost.

Anyway I agree on the batteries, but they do have a place when run in parallel on bus bars etc.. and that's for short high current draw settings like sanctioned SPL events where you're required to run the car through the lanes with the engine off and rely on battery power. When you have 20Kw of amplifiers in an SUV, you just can't do that off of a starter battery haha
 

Gold Member
Username: Mendonmafia

USA

Post Number: 2032
Registered: Aug-06
so what do you do when you cant get any more alternator, ie have the largest alt for your vehicle and cant add more?

rob wollcott (thorshammer, ca.com) used to run 14k daily on 200 amp alt, and 5 hc2400's. he has since upgraded to300 amp alt but still shouldn't be "enough" for 14k (pretty sure he has28k now).

someone once told me that you can add many runs of wire and that will some how store electricity in the wires. supposedly people who compete in the stock classes and can only have one battery will run like 50 sets of 1/0 from the battery to the back. I personally dont believe this but it almost makes sense, maybe someone with more knowledge can enlighten.
 

Platinum Member
Username: Glasswolf

Lexington, SC USA

Post Number: 13478
Registered: Dec-03
You run multiple alternators on a custom accessory bracket with a serpentine belt, in addition to multiple runs of multi-0 AWG wire for both pos(+) and ground(-) for all the power lines, and you run a bank of batteries to act as voltage stabilization for the rectification of the AC voltage produced by the alternators as well as acting to power the system when the engine is turned off.

If the wire had enough capacitance to store current that way, you'd have bigger issues to deal with as a result. What the multiple runs can do however, is reduce resistance and inductance in the wiring to decrease voltage drop between the power source and amplifiers.
 

Gold Member
Username: Tejcurrent

Post Number: 2236
Registered: Apr-07
When you can't add more alternator, and batteries aren't cutting it, get a bigger vehicle :P

Seriously.
 

Platinum Member
Username: Glasswolf

Lexington, SC USA

Post Number: 13487
Registered: Dec-03
that or do what factory demo vans used to do and run the system on 220VAC from a wall outlet instead.
 

Silver Member
Username: Cwruck

Post Number: 123
Registered: Feb-10
so what will it take to run at least 1200 watts? would a stock alt with an optima like a yellow top d31 work? its like the biggest yellow top optima has.
or do you absolutely have to upgrade the alt?
i see many people on youtube that run much more than 1200 watts with a stock alt, ive even seen a few that claim they have 10,000 watts and it looks like it is close because they have high scores like 158s and the subs are just destroying their vehicles.
i understand its probably horrible to do that, but im looking at running 1200-1500 watts at the most
 

Platinum Member
Username: Glasswolf

Lexington, SC USA

Post Number: 13497
Registered: Dec-03
http://www.glasswolf.net/papers/index.html

read the first two, and the last link listed below the heading "Electrical."

This will answer your question.
 

Silver Member
Username: Sleste8

Shelbyville, MI United States

Post Number: 159
Registered: Mar-10
instead of starting a new thread.....

what size fuse should i use between my alt and my battery? ive read it's best to use a fuse rated to the max amps of the wire, and ive read you should use a fuse that matches the amp output of your alt.

also ive read you should put the fuse closer to the alt, and other places say put it close to the battery?

how do you guys choose?
tyvm
 

Platinum Member
Username: Glasswolf

Post Number: 13612
Registered: Dec-03
match the fuse to the wire peak capacity or the alternator output. either one.
it's really just there to prevent a dead short. nothing more.
I generally put mine about in the middle, really. whatever isn't too close to any belts or sources of heat.
 

Silver Member
Username: Sleste8

Shelbyville, MI United States

Post Number: 160
Registered: Mar-10
ok, sounds great. thanks.

ohh, and ive seen many people do this with no fuse at all, they say it's overkill. but even the factory wire goes to the fuse block. how could they think this isn't needed? i guess ill be the one laughing when they tell me there car burnt to the ground.
 

Platinum Member
Username: Glasswolf

Post Number: 13615
Registered: Dec-03
exactly. I over-engineer things anyway, but yeah the thing is if that wire under the hood gets warm from the engine heat, and gets softer (which happens) it can sag if it's not wire tied in place. If the wire sags enough, it could come into contact with the heads, block, radiator, etc.. and melt through the wire insulation, then you have a dead short to the alternator or battery. That's instant heat and yeah.. fire under the hood. That sort of fire can spread very quickly and destroy the entire car in short order.
The response I get is "I've had my "big 3" for 2 years now and never had a problem!"
Good for you, I tell them.. I'd still rather be safe than sorry when I have a 300A alternator, and a bank of batteries in the trunk, and a few kilowatts worth of amplifiers sucking massive current through 1/0 gauge wire. Take your chances. I'd rather spend the extra $20 for the fuse holder and the fuse, or for a circuit breaker.

A lot of people don't believe in fused distribution blocks, either. They figure the amplifier's own fuses are good enough. I still like the fused blocks. I've had wires come loose in a car before. It causes a lot of problems. Heck, some people go so far as to fuse their speaker wires in case a sub shorts out, to protect the amp at both ends.
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